The diagram shows the two-module system. On the single-module system the IDM is integrated in the PCM.
1 IDM
2 PCM
3 CKP signal
4 Separate IDM/PCM cable for transmission of the CKP signal
For the engine to start, the battery voltage must be > 9V. In addition, a starter speed of 190 โฆ 225 rpm (depending on vehicle and engine version) is required.
During the starting process the PCM compares the engine load map with the incoming sensor signals (CHT, MAP, IAT).
At the same time the IDM compares the sensor signals fuel pressure, fuel temperature, CKP and CMP with the data in the map tables.
Afterwards the IDM sends the CKP signal via a separate cable (already digitized) to the PCM.
The reason for the separate connection to the PCM (i.e. bypassing the CAN data bus) is the high priority with which the CKP signal has to be transmitted to the PCM. This ensures that the injected fuel quantity and the injection timing can be calculated as quickly as required.
Note on checking the CKP signal if the engine does not start:
โข Using the WDS data logger, check in the “PCM” section to see if the CKP signal is present. If it is present, check in the “ICU” section to see if the signal is also present here. If the signal is not present here, the separate cable from the IDM to the PCM may be faulty.
The diagram shows the two-module system. On the single-module system the IDM is integrated in the PCM.
1 Cam for identifying cylinder 1
2 CMP sensor
3 CKP sensor
4 Tooth gap on sensor ring for crankshaft position
5 IDM
6 Injected fuel quantity and injection timing
7 Engine speed signal (already digitized)
8 Separate cable to IDM/PCM
9 PCM
10 Synchronization of CKP-/CMP signal
The CMP signal is transmitted by the IDM to the PCM via the CAN data bus at the same time as the CKP signal. In the PCM the CKP signal is then synchronized with the CMP signal.
Note:
โข Synchronization is of greater significance for the common-rail injection system. By comparing the position of the crankshaft (CKP) and the camshaft (CMP) cylinder 1 is identified and the injection sequence is thus determined.
โข Injection can only be carried out if synchronization has been successfully completed (cylinder 1 identified).
โข If the CMP signal is missing, the fuel injection release is not issued, in other words, the engine does not start.
In older vehicles (at the time of going to press) if the CMP signal is missing no diagnostic trouble code is stored in the system. In newer vehicles this has been implemented into the strategy so that if the CMP signal is missing a diagnostic trouble code is stored.
After synchronization has been completed successfully, the PCM calculates the injected fuel quantity and the injection timing.
Note:The PCM has a protective function. If the PCM detects faulty input signals or other faults which could result in damage or even destruction of the system, the fuel quantity is set to 0 so that it is not possible to start the engine.
The calculated injected fuel quantity, together with the injection timing, is sent to the IDM as a complete block. The IDM splits the block into specific pilot and main injection quantities.
After the block has been split, a start release is issued. Fuel is injected and the engine starts to fire.
Note:
โข The engine is not yet idling!
โข The engine is merely starting up.
Protective zone for dual mass flywheel at approximately 400 rpm.
When an engine speed of 400 rpm is reached, oscillation of the dual mass flywheel is particularly high โ there is a risk of damaging the dual mass flywheel.
If for any reason this engine speed is not exceeded, the system sets the injected fuel quantity to 0 and the engine cuts out.
Faulty dual mass flywheel
A faulty dual mass flywheel (for example worn springs in the dual mass flywheel) usually increases the oscillations; these are also at their highest at an engine speed of 400 rpm. This increase in oscillations is detected by the CKP sensor. As a result, the system sets the injected fuel quantity to 0 and the engine cuts out.
Monitoring of engine operation The engine restriction check is active at engine speeds between 450 … 700 rpm. In this phase, the system checks to see if the engine is running properly.
Besides a possible stiffness of the engine itself, the running can also be braked by defective components/ancillary components. Such defective components/ancillary components could include:
โข blocked A/C compressor,
โข blocked power steering pump,
โข faulty fuel injector, faulty engine component (engine running on only three cylinders).
In this case, the injected fuel quantity is not increased any further which means that engine speed does not increase, even if the accelerator pedal is pressed.